The present invention generally relates to a heat shield brick, in particular a heat shield brick for lining a combustion chamber wall. The brick may have a hot side which can be exposed to a hot medium, a wall side opposite the hot side, and a peripheral side which can adjoin the hot side and the wall side, and a peripheral-side surface. The present invention also generally relates to a combustion chamber having an inner combustion chamber lining and to a gas turbine.
A thermally and/or thermomechanically highly loaded combustion space, such as, for example, a furnace, a hot gas duct, or a combustion chamber of a gas turbine, in which a hot medium is produced and/or directed is provided with an appropriate lining for protection from excessive thermal stressing. The lining is normally made of a heat-resistant material and protects a wall of the combustion chamber from direct contact with the hot medium and the associated high thermal loading.
U.S. Pat. No. 4,840,131 relates to a fastening of ceramic lining elements on a wall of a furnace. In this case, a rail system which is fastened to the wall and has a plurality of ceramic rail elements is provided. The lining elements can be mounted on the wall by the rail system. Further ceramic layers may be provided between a lining element and the wall of the furnace, inter alia a layer of loose, partly compressed ceramic fibers, this layer having at least approximately the same thickness as the ceramic lining elements or a greater thickness. The lining elements in this case have a rectangular shape with a planar surface and are made of a heat-insulating, refractory ceramic fiber material.
U.S. Pat. No. 4,835,831 likewise deals with the application of a refractory lining to a wall of a furnace, in particular to a vertically arranged wall. A layer consisting of glass fibers, ceramic fibers or mineral fibers is applied to the metallic wall of the furnace. This layer is fastened to the wall by metallic clips or by adhesive. A wire mesh net with honeycomb meshes is applied to this layer. The mesh net likewise serves to prevent the layer of ceramic fibers from falling down. By means of a suitable spraying process, a uniform closed surface of refractory material is applied to the layer thus fastened. The method described largely prevents a situation in which refractory particles striking during the spraying are thrown back, as would be the case with direct spraying of the refractory particles onto the metallic wall.
A ceramic lining of the walls of thermally highly stressed combustion spaces, for example of gas-turbine combustion chambers, is described in EP 0 724 116 A2. The lining consists of wall elements of high-temperature-resistant structural ceramic, such as, for example, silicon carbide (SiC) or silicon nitride (Si3N4). The wall elements are elastically fastened to a metallic supporting structure (wall) of the combustion chamber in a mechanical manner by means of a central fastening bolt. A thick thermal insulating layer is provided between the wall element and the wall of the combustion space, so that the wall element is at a corresponding distance from the wall of the combustion chamber. The insulating layer, which is about three times as thick in relation to the wall element, is made of a ceramic fiber material which is prefabricated in blocks. The dimensions and the external shape of the wall elements can be adapted to the geometry of the space to be lined.
Another type of lining of a thermally highly loaded combustion space is specified in EP 0 419 487 B1. The lining includes heat shield elements which are mechanically mounted on a metallic wall of the combustion space. The heat shield elements touch the metallic wall directly. In order to avoid excessive heating of the wall, e.g. as a result of direct heat transfer from the heat shield element or by introducing hot medium into the gaps formed by the heat shield elements adjoining one another, cooling air, the xe2x80x9csealing airxe2x80x9d, is admitted to the space formed by the wall of the combustion space and the heat shield element. The sealing air prevents the penetration of hot medium up to the wall and at the same time cools the wall and the heat shield element.
WO 99/47874 relates to a wall segment for a combustion space and to a combustion space of a gas turbine. Specified in this case is a wall segment for a combustion space which can be acted upon by a hot fluid, e.g. a hot gas, having a metallic supporting structure and a heat protection element fastened to the metallic supporting structure. Inserted between the metallic supporting structure and the heat protection element is a deformable separating layer which is intended to absorb and largely compensate for possible relative movements of the heat protection element and the supporting structure. Such relative movements may be caused, for example, in the combustion chamber of a gas turbine, in particular in an annular combustion chamber, by different thermal expansion behavior of the materials used or by pulsations in the combustion space, which may arise during irregular combustion for producing the hot working medium or by resonance effects. At the same time, the separating layer causes the relatively inelastic heat protection element to rest in a more planar manner overall on the separating layer and the metallic supporting structure, since the heat protection element partly penetrates into the separating layer. The separating layer can thus compensate for production-related unevenness at the supporting structure and/or the heat protection element, which unevenness may lead locally to an unfavorable concentrated introduction of force.
An embodiment of the present invention is based on the observation that, in particular ceramic, heat shield bricks, on account of their requisite flexibility with regard to thermal expansions, are often only inadequately protected against mechanical loads, such as shocks or vibrations for example.
An object of the present invention is accordingly to specify a heat shield brick which ensures high operating reliability with regard to both unrestricted thermal expansion and stability relative to mechanical, in particular shock-like, loads. A further object of the present invention is to specify a combustion chamber having an inner combustion chamber lining and to specify a gas turbine having a combustion chamber.
An embodiment of the present invention provides a heat shield brick, in particular for lining a combustion chamber wall, having a hot side which can be exposed to a hot medium, a wall side opposite the hot side, and a peripheral side which adjoins the hot side and the wall side and has a peripheral-side surface. A tension element prestressed in the peripheral direction is provided on the peripheral side, a compressive stress normal to the peripheral-side surface being produced.
An embodiment of the present invention provides lasting protection for heat shield bricks against high accelerations as a result of shocks or vibrations. In this case, the present invention is already based on the knowledge that steady and/or transient vibrations in a combustion chamber wall induce corresponding vibrations in combustion chamber bricks as normally used for lining said combustion chamber wall. In this case, considerable accelerations above a limit acceleration may occur, in particular in the event of resonance, in the course of which the heat shield bricks lift from the combustion chamber wall and consequently strike again. Such striking on the solid or also partly damped combustion chamber wall leads to very high forces on the heat shield bricks and may cause considerable damage, e.g. fracture of the latter. There is also the high thermal loading of the heat shield brick on account of the admission of a hot medium to the heat shield brick during operation. Incipient cracks may therefore occur on both the wall side and the hot side of the heat shield brick, there also being the risk of material being released from the heat shield brick. This leads to a considerable reduction in the endurance of a heat shield brick, in particular because such incipient cracks may lead to a crack through the material and thus to a fracture and thus failure of the entire heat shield brick. Consequently, there is the risk of fragments passing into the combustion space and causing massive damage to further components of the combustion chamber or, for example during use in a gas turbine, to the sensitive blading region having turbine blades.
With the proposed heat shield brick having a tension element prestressed in the peripheral direction at the peripheral side, extremely efficient protection, with long-term stability, for a heat shield brick is specified for the first time. The tension element is prestressed in the peripheral direction, a certain compressive stress normal to the peripheral-side surface being produced. By this normal force, which is directed in the direction of the interior of the heat shield brick in its center, the heat shield brick is secured even at very low normal forces. In this way, an incipient crack in the material, for example as a result of shock loading, is effectively countered. Existing incipient cracks in the material, given an appropriate arrangement and configuration of the tension element, cannot develop or expand, or can only do so to a limited extent. The tension element holds the heat shield brick together, as it were, and protects it against incipient cracks in the material, on the one hand, and in particular against a crack right through the material, on the other hand. In addition, the risk of smaller or larger fragments being released or falling out in the event of a possible crack through the material is effectively countered.
By the provision of the tension element on the peripheral side of the heat shield brick, vibrations and/or shock loads with a component normal to the peripheral-side surface are advantageously damped. Given an appropriate configuration and choice of material for the tension element, the damping constant can be set in accordance with the loads which occur. Such shock loads normal to the peripheral-side surface may occur, for example, in the arrangement of a plurality of heat shield bricks as a result of the relative movement of adjacent heat shield bricks. By this damping, prolonged use of the heat shield brick can be ensured.
Especially advantageous is the increase in the passive safety of the combustion chamber brick compared with the conventional configurations. An incipient crack in the material or a crack through the material is countered, release of fragments of the combustion chamber brick being largely prevented in the event of a crack through the material.
Furthermore, the configuration of the heat shield brick with the tension element results in the advantage of problem-free prefabrication and ease of assembly of the heat shield brick, for example for fitting in a combustion chamber wall. The tension element is simply attached at the peripheral side and prestressed in the peripheral direction according to requirements. Separate damping and/or protective elements, as can additionally be found in conventional heat shield bricks, require a considerably greater assembly and adjusting effort compared with the heat shield brick of the invention. During an inspection, possibly only the heat shield brick has to be exchanged, but not additional protective elements. This high flexibility on the one hand and the attainable endurance of the heat shield brick on the other hand are also especially advantageous from the economic point of view. In particular, inspection or maintenance intervals for the heat shield brick, for example when used in a combustion chamber of a gas turbine, are extended. If a heat shield brick fractures, operation need not be stopped immediately for inspecting the plant, since, on account of the increased passive safety, continued operation up to the regular inspection interval or beyond this is possible.
The compressive stress which is produced normal to the peripheral-side surface is advantageously adjustable by appropriate prestressing of the tension element.
According to an embodiment of the present invention, the tension element extends at least zonally in the peripheral direction. As a result of the respective geometry of the heat shield brick, for example in the form of prisms having a polygonal base area, various regions can be formed on the peripheral side, which has the peripheral-side surface. So that the tension element can develop its full effect for increasing the passive safety of the combustion chamber brick, it is appropriate for the tension element to extend at least zonally, in particular even so as to overlap in regions, in the peripheral direction. Thus a corresponding compressive stress normal to the peripheral-side surface can be produced in a region.
A plurality of tension elements are preferably provided. The arrangement and configuration of the tension elements on the peripheral side can be effected in a very flexible manner by the use of a plurality of tension elements. By the use of a plurality of tension elements, critical regions of the heat shield brick, for example corners or edges, in which an incipient crack or rupture, or release of possible fragments, would be expected, can be specifically protected. As a result, the operational reliability of the heat shield brick is further increased.
According to an embodiment of the present invention, a tension element completely encloses the peripheral-side surface. By this configuration, a protective normal force on the peripheral-side surface is ensured over the entire periphery of the heat shield brick. A complete ring closure, as it were, is achieved, the heat shield brick overall being advantageously passively protected in a comprehensive manner by the forces directed locally into the interior of the heat shield brick. Even one tension element like this which completely encloses the peripheral-side surface can ensure this. Depending on the loading case, however, a plurality of such tension elements completely enclosing the peripheral-side surface can be attached.
The tension element preferably encloses the peripheral-side surface several times. A tension element enclosing the peripheral surface several times correspondingly multiplies the protective effect of the tension element, the protective forces directed normal to the peripheral-side surface being increased. By this multiple enclosure, the tension element forms, as it were, multiple reinforcement of the heat shield brick on the peripheral side. By this multiple protection, especially high operating reliability is achieved, with the economic advantages already discussed further above.
The peripheral side also preferably has a peripheral groove in which the tension element engages. In this case, the peripheral groove is advantageously formed over the entire periphery on the peripheral side, for example by appropriate stock removal from the heat shield brick or by shaping the peripheral groove when producing the heat shield brick from a, for example ceramic, molding compound. The heat shield brick is protected in a very effective manner by the engagement of the tension element in the peripheral groove, the tension element in the peripheral groove being additionally protected from direct admission of a hot gas, as is provided in the operating case. Furthermore, the peripheral groove protects the tension element from falling out or, provided a plurality of tension elements are used, protects the tension elements engaging in the peripheral groove from falling out. The peripheral groove advantageously extends over the entire periphery of the heat shield brick. In an alternative configuration, however, it is possible for the peripheral groove not to be formed over the entire periphery of the heat shield brick but only in a section of the peripheral side which can be selected in each case.
At least one further peripheral groove which is at a distance from the peripheral groove is also preferably provided, a tension element engaging in the further peripheral groove. In this case, the peripheral groove may be provided, for example, on that end of the peripheral side which faces the hot side of the combustion chamber brick, whereas the further peripheral groove is provided on that end of the peripheral side which faces the wall side. Multiple protection with peripheral grooves in which at least one tension element engages in each case is thereby ensured, the advantages discussed for the peripheral groove being accordingly obtained to an increased extent.
The tension element is advantageously designed as a cord or strip, in particular such as to be braided or woven. To apply an adjustable tensile force by means of prestressing, the cord or the strip optionally has a certain elasticity. A suitable tension element is also a wire or a wire braid. For the tension element, therefore, recourse may be had to largely conventionally obtainable primary materials, a factor which makes it easier to realize the heat shield brick having the tension element and which, from the cost point of view, also makes use within limits appear very interesting.
In this case, conversion of conventional heat shield bricks according to an embodiment of the present is also possible. The tension elements in the form of a cord or a strip, which are, for example, braided or woven, can be applied to existing conventional heat shield bricks in a simple manner.
According to an embodiment of the present invention, the tension element is made of a ceramic material, in particular of a ceramic fiber material. Ceramic material is resistant to high temperatures and is oxidation- and/or corrosion-resistant and is therefore eminently suitable for the use as a heat shield brick in a combustion chamber. In this case, cords and/or strips preferably consist of ceramic fibers which are suitable for use at up to 1200xc2x0 C. The chemical composition of these fibers is, for example, 62% by weight of Al2O3, 24% by weight of SiO2 and 14% by weight of B2O3. The fibers in this case are composed of a multiplicity of individual filaments, the filaments having a diameter of about 10 to 12 xcexcm. The maximum crystallite size in these ceramic fibers is typically 500 nm. Woven fabrics, knitted fabrics, or braids of the desired size and thickness, or even cords or strips, can be produced from the ceramic fiber material in a simple manner. With a tension element of such design, lasting protection of the heat shield brick, even at very high operating temperatures, as occur, for example, in a combustion chamber of a gas turbine, is ensured.
The tension element is preferably at least partly adhesively bonded to the heat shield brick. The adhesive bonding additionally protects the tension element from possible release and correspondingly increases the endurance. When the tension element is adhesively bonded to the heat shield brick, both a conventional adhesive and a high-temperature-resistant adhesive may be used. Silica-based adhesives, which have excellent adhesive properties and a high temperature resistance, may also be used. The use of ceramic or metallic materials for the tension element proves to be especially advantageous for the connection, especially in the case of a ceramic cord or a ceramic strip, since the latter, on account of the fabric structure, has a certain air permeability (porosity), a factor which promotes a sound connection between the tension element and the heat shield brick. The adhesive bonding is especially effective if the configuration with the peripheral groove, in which a tension element engages, is selected. As a result, the adhesive for the adhesive bonding can be let into the peripheral groove, as a result of which an especially sound connection can be produced. In this case, the adhesive may be introduced locally at various points of the peripheral groove or may wet the peripheral groove, for example in the groove root, in certain regions or completely. By the adhesive bonding, the tension element becomes, as it were, an integral component of the heat shield brick, in which case the adhesive bonding can be executed in such a way as to be releasable or, if desired, permanent for an inspection case.
The heat shield brick is preferably made of a ceramic parent material, in particular of a refractory ceramic. By the selection of a ceramic as parent material for the heat shield brick, the use of the heat shield brick up to very high temperatures is reliably ensured, in which case at the same time oxidative and/or corrosive attacks, as occur when a hot medium, e.g. a hot gas, is admitted to the hot side of the heat shield brick, are to a very large extent harmless for the heat shield brick. The tension element can advantageously be effectively connected to the ceramic parent material of the heat shield brick. In this case, the firm connection, as already discussed above, may be configured as a releasable connection. A suitable connection, in addition to the adhesive bonding, is the attachment of the tension element to the peripheral side by means of suitable fastening elements, e.g. by clipping or by a screwed connection. By the selection of a tension element which is made at least partly of a ceramic material, good adaptation to the ceramic parent material of the heat shield brick with regard to the thermomechanical properties is also achieved. By the firm connection between the tension element and the parent material, the heat shield brick is advantageously configured so as to form a type of composite with the tension element. The heat shield brick thus has a compact type of construction and structure which has exceptionally high endurance and passive safety even during high thermal and/or mechanical loading. This is especially advantageous when the heat shield brick is used in a combustion chamber, because, even after an incipient crack or crack through the material, the heat shield function of the heat shield brick continues to be ensured; in particular, it is reliably ensured that no fragments can pass into the combustion space.
In economic terms, this results, on the one hand, in the advantage that no exceptional maintenance and/or inspection of a combustion chamber having the heat shield brick is necessary in the normal operating case. On the other hand, the heat shield brick, in the event of special incidents, has emergency running properties, so that consequential damage to a turbine, for example the blading, can be avoided.
The combustion chamber may be operated at least with the normal maintenance cycles, although the service life can also be prolonged on account of the passive safety increased with the tension element.
The object which relates to a combustion chamber is achieved according to the present invention by a combustion chamber having an internal combustion chamber lining which has heat shield bricks according to the above explanations.
The object which relates to a gas turbine is achieved according to the present invention by a gas turbine having such a combustion chamber.
The advantages of such a combustion chamber or of such a gas turbine follow in accordance with the explanations in respect of the heat shield brick.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the present invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.